This invention relates to roll-up doors of the type employing flexible sheets forming curtains for closing doorways and, in particular, to bottom bar apparatus for roll-up doors which are mountable on the lower ends of the door curtains.
It is well known in the industrial and commercial door industry to provide a flexible roll-up door that can be used to provide a passageway barrier in various types of facilities to accommodate the access of trucks, forklifts and other equipment to a facility or building or to provide passageway barriers within the facility or building. A flexible roll-up door typically consists of a synthetic rubber or fabric curtain which acts as a barrier across the passageway and which is attached across its top edge to a rigid steel pipe spanning the width of the passageway. This pipe is known as a drive barrel and it forms part of a curtain winding mechanism capable of raising or lowering the roll-up door as required.
It is also known to fit the lower end of the door curtain with some form of bottom bar which provides rigidity to the bottom edge of a door that makes contact with the ground. It is known that this bottom bar must be of sufficient rigidity to maintain adequate straightness of the curtain for the operation of the door. Also the bar is configured to have an adequate weight or mass to provide sufficient gravitational force to pull the curtain to the ground. It is also known to provide this bottom bar with reversing, safety and/or sealing devices.
Recent U.S. Pat. No. 7,516,770 issued Apr. 14, 2009 to TNR Industrial Doors Inc. describes a roll-up door assembly that includes a flexible curtain which can be made of synthetic rubber or fabric, a curtain winding mechanism and two guide members which extend vertically on opposite sides of the doorway. Opposite side edge sections of the curtain are movable in respective guide members. Each guide has inner and outer wall sections with each wall section having an inwardly projecting, longitudinal rib. The two ribs of each guide form an elongate slot that receives a side edge section of the curtain and spaced-apart pairs of curtain lock members are mounted on and distributed along each side edge section of the curtain. These lock members act to hold the side edges of the curtain within their respective guides but in a releasable manner. This known roll-up door is also provided with a bottom bar made with a couple of steel angle members that are secured to a bottom edge section of the curtain by means of bolts. The bar itself does not extend into the metal guide members for the door but plastic arms can be fastened to the ends of the bottom bar so as to extend into the guide members.
U.S. Pat. No. 5,765,622 issued Jun. 16, 1998 to Thruways Doorsystems Inc. describes a so-called damage minimizing roll-up door made with a continuous flexible curtain that has a bottom bar mounted along its lower edge. The bottom bar is releasably connected to guide structures mounted on opposite sides of the door opening. The bottom bar is constructed of two bar portions located on opposite faces of the curtain and secured to each other by bolts. The outer bottom bar portion has a notch formed therein and a retainer is affixed in this notch. The retainer is defined by a clip that includes a base web fastened to the outer bottom bar portion. The clip includes a pair of retaining clip arms which are flexible and biased. Each clip arm has a profile portion that is arcuate to accommodate a retaining tube sized to receive a roller shaft on which a roller is mounted. This roller is movable up and down in a roller guideway. The retainer of this patent is designed so that an impact force on the curtain will result in the bottom bar releasing or breaking away from the rollers located at its opposite ends.
There is a need for an improved bottom bar apparatus for a roll-up door made with a flexible sheet that forms a curtain which can be constructed at a reasonable cost and which better enables the roll-up door to withstand windloads on one side of a door curtain or air pressure on one side of the curtain that is greater than the air pressure on the opposite side.